Quiescent current control circuit for high-power amplifiers

ABSTRACT

A control circuit for controlling a bias circuit coupled to an amplifier is disclosed. An exemplary bias control circuit comprises means for receiving a control voltage, and means for actively adjusting an equivalent resistance of the bias control circuit responsive to the control voltage, wherein the equivalent resistance is established between the first node and a reference voltage. In one embodiment, when the control voltage is increased, the equivalent resistance is gradually decreased and a current drawn by the bias control circuit is gradually increased, resulting in a quiescent current of the amplifier transistor being gradually increased.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally in the field of semiconductors. Morespecifically, the invention is in the field of semiconductor circuitsand amplifiers.

2. Related Art

Amplifiers based on bipolar technology are widely used in a variety ofapplications, including wireless communication, such as radio frequency(“RF”) communication, for example. Bias circuits perform an importantfunction by supplying a base bias current to bipolar transistors forcontrolling the operation modes of the bipolar transistors inamplifiers.

Digital mode control circuits have been used to reduce current and powerconsumption for low power mode operation in high-power amplifiers.Digital mode controls circuits, however, have a single and abrupttransition point from low power mode to high power mode, whichsubstantially limits current consumption savings, particularly duringvery low power mode operation.

In an effort to improve current consumption savings, CMOS circuitry inan additional CMOS die have been employed in high-power amplifiers. Withthis arrangement, CMOS circuitry can provide improved analog controlvoltage into the base bias of the bipolar transistor of the amplifier,resulting in a substantially continuous quiescent current transitionfrom a very low power level. In this way, current consumption can begreatly reduced even at low power modes. The addition of a separate CMOSdie to the amplifier, however, results in increased device size andincreased costs, both of which are undesirable.

Accordingly, there is a strong need in the art for a quiescent currentcontrol circuit for high-power amplifiers.

SUMMARY OF THE INVENTION

The present invention is directed to a quiescent current control circuitfor high-power amplifiers. In one exemplary embodiment, the controlcircuit controls a bias circuit coupled to an amplifier, such as ahigh-power CDMA amplifier. The bias circuit includes a first biastransistor, a second bias transistor, and a third bias transistor,wherein a base of the amplifier transistor is coupled to an emitter ofthe second bias transistor, a base of the second bias transistor iscoupled to a base of the first bias transistor and to a collector of thethird bias transistor, and a base of the third bias transistor iscoupled to an emitter of the first bias transistor and to the biascontrol circuit at a first node.

In one embodiment, the bias control circuit comprises means forreceiving a control voltage, and means for actively adjusting anequivalent resistance of the bias control circuit responsive to thecontrol voltage, wherein the equivalent resistance is establishedbetween the first node and a reference voltage, such as ground. Forexample, in one embodiment, when the control voltage is increased, theequivalent resistance is gradually decreased and a current drawn by thebias control circuit is gradually increased, resulting in a quiescentcurrent of the amplifier transistor being gradually increased. As such,continuous quiescent current control of the amplifier transistor isachieved, resulting in significant current and power consumptionsavings.

According to one embodiment, the bias control circuit, the bias circuitand the amplifier transistor are based on bipolar technology. As such,the bias control circuit, the bias circuit and the amplifier transistorcan be integrated into a single die, resulting in significant reductionin device size and device cost.

Other features and advantages of the present invention will become morereadily apparent to those of ordinary skill in the art after reviewingthe following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit diagram of an exemplary bias circuit for ahigh-power amplifier according to one embodiment of the presentinvention.

FIG. 2 shows a circuit diagram of an exemplary control circuit accordingto one embodiment of the present invention.

FIG. 3 shows a circuit diagram of an exemplary control circuit accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a quiescent current control circuitfor high-power amplifiers. The following description contains specificinformation pertaining to the implementation of the present invention.One skilled in the art will recognize that the present invention may beimplemented in a manner different from that specifically discussed inthe present application. Moreover, some of the specific details of theinvention are not discussed in order not to obscure the invention. Thespecific details not described in the present application are within theknowledge of a person of ordinary skill in the art.

The drawings in the present application and their accompanying detaileddescription are directed to merely exemplary embodiments of theinvention. To maintain brevity, other embodiments of the invention whichuse the principles of the present invention are not specificallydescribed in the present application and are not specificallyillustrated by the present drawings.

Referring to FIG. 1, there is shown a circuit diagram of exemplary biascircuit 102 including control circuit 106 according to one embodiment ofthe present invention. In FIG. 1, bias circuit 102 is coupled to andsupplies base bias current 108 (“Ib 108”) to amplifier transistor 110 ofamplifier 104. Amplifier 104 may, for example, be a high-poweramplifier, such as a high-power CDMA handset amplifier, and amplifiertransistor 110 may for example, be a large heterojunction bipolartransistor (“HBT”). As discussed below, control circuit 106 is based onbipolar technology and be integrated into the same die as bias circuit102 and amplifier 104. Also discussed below, control circuit 106achieves dynamic and continuous control of quiescent current 112 (“Icq112”) of amplifier transistor 110, resulting in significantly reducedcurrent and power consumption.

As shown in FIG. 1, bias circuit 102 comprises bias transistors 114, 116and 118, and resistors 120 and 122. Bias transistors 114, 116 and 118comprise bipolar transistors, wherein a base of bias transistor 114 isconnected at node 128 to a base of bias transistor 116 and to acollector of bias transistor 118. Bias transistor 114 further has anemitter connected at node 126 to control circuit 106 and to a base ofbias transistor 118. An emitter of bias transistor 118 is connected to areference voltage, such as ground 132. Bias transistor 116 further hasan emitter connected at node 130 to a base of amplifier transistor 110.An emitter of amplifier transistor 110 is connected to a referencevoltage, such as ground 132.

According to one embodiment, resistor 120 is approximately 1 to 2kiloOhms (kΩ) and is connected across reference voltage (“Vref”) 124 andnode 128, and resistor 122 is approximately 0.5 to 1 kΩ and is connectedacross node 130 and a reference voltage, such as ground 132. Accordingto another embodiment, resistor 122 may be omitted, wherein the emitterof bias transistor 116 is connected only to the base of amplifiertransistor 110. Nodes 134, 136 and 138 may be connected to a biasvoltage or may be directly connected to a supply voltage (“VCC”), as isknown in the art.

Control circuit 106 is connected across node 126 and a referencevoltage, such as ground 132. As shown in FIG. 1, control circuit 106comprises bias control transistor 140 and resistors 142, 144, 146 and148. Resistor 142 is connected across node 126 and node 158 and,according to one embodiment, is approximately 2 kΩ. Resistor 144 isconnected across node 158 and a reference voltage, such as ground 132and, according to one embodiment, is approximately 100 kΩ. Resistor 146is connected across an emitter of bias control transistor 140 and areference voltage, such as ground 132 and, according to one embodiment,is approximately 100 Ω. Bias control transistor 140 comprises a bipolartransistor and has a collector connected to node 158 and a baseconnected to node 160. Resistor 148 is connected across node 160 and acontrol voltage (“Vcont”) 156 and, according to one embodiment, isapproximately 10 kΩ.

In operation, control circuit 106 receives Vcont 156 and provides a“reference” resistance corresponding to an equivalent resistance (“Req”)across node 126 and ground 132. Req determines the status of biascircuit 102, which in turn determines the status of Icq 112 of amplifier104. In control circuit 106, bias control transistor 140 operates as anactive resistor controlled by Vcont 156, such that as Vcont 156 isincreased from a low level to a high level, Req is gradually decreased.Vcont 156, for example, may have a low level of approximately 0 to 1.1volts (“V”) and a high level of approximately 2 to 3 V. Resistor 142establishes the primary resistance of Req for high mode operation andoperates to restrict Icq 112 at high Vcont 156, and resistor 144establishes the primary resistance of Req for low mode operation andoperates for baseline Icq 112 at very low Vcont 156.

With this arrangement, as Vcont 156 is increased from a low level, biascontrol transistor 140 is gradually turned on, resulting in a gradualincrease of collector current (“Ic”) 162 of bias control transistor 140.As Ic 162 is gradually increased, Req of control circuit 106 isdynamically reduced such that control circuit 106 draws increasedcurrent 164, resulting in a decrease in base current (“Ib”) 166 and Ic168 of bias transistor 118. Decreased Ic 168 results in increased 1 b170 and Ic 172 of bias transistor 116, further resulting in increased Vbof amplifier transistor 110 at node 130, and further in increased Ib 108and Icq 112 of amplifier transistor 110.

Due to the particular arrangement of control circuit 106 and biascircuit 102, significantly improved analog control over Vb of amplifiertransistor 110 by control circuit 106 is achieved, such that continuousIcq 112 transition from a very low power level can be provided, whichresults in significant current savings. Since control circuit 106 isbased on bipolar technology, control circuit 106 may be integrated in tothe same die as bias circuit 102 and amplifier 104, resulting insubstantial cost savings and significantly reduced device size.

As shown in FIG. 1, control circuit 106 may further include temperaturecompensation circuit 150 comprising resistor 152 and diode 154. Resistor152 is connected across node 160 and an anode of diode 154 and,according to one embodiment, is approximately 2 to 5 kΩ. Diode 154 may,for example, be an HBT diode, and further has a cathode connected to areference voltage, such as ground 132. In the absence of temperaturecompensation circuit 150, at high temperatures, the requisite forwardbias voltage (corresponding to the base-to-emitter voltage (“Vbe”)) ofbias control transistor 140 drops, resulting in an increase in Ic 162 ofbias control transistor 140 and a corresponding decrease in the Req ofcontrol circuit 106. However, with resistor 152 and diode 154 coupled tothe base of bias control transistor 140 at node 160, diode 154 offsetsany increase in Ic 162 by drawing a corresponding increased current 174from node 160 to ground 132, since at high temperatures, the requisiteforward bias voltage for diode 154 decreases for the same reason thatthe requisite forward bias voltage of bias control transistor 140 drops.As a result, greater control and accuracy of Req of control circuit 106are achieved even at high temperatures, which, as discussed above,provides significantly improved analog control over Vb of amplifiertransistor 110 and improved continuous control of Icq 112 of amplifiertransistor 110, resulting in significantly reduced current and powerconsumption.

Referring now to FIG. 2, exemplary control circuit 206 according anotherembodiment of the present invention is shown. Control circuit 206 may beused to control bias circuit 102 of FIG. 1 and to provide continuouscontrol of quiescent current 112 of amplifier transistor 110 asdescribed above, wherein control circuit 206 replaces control circuit106 of FIG. 1, and wherein node 226, Vcont 256 and ground 232respectively corresponds to node 126, Vcont 156 and ground 132 of FIG.1.

As shown in FIG. 2, control circuit 206 comprises bias controltransistor 240, resistors 242, 248, 276, 278 and 280, and diode 282.Resistor 242 is connected across node 226 and node 258 and, according toone embodiment, is approximately 2 kΩ. Resistor 276 is connected acrossnode 258 and node 284 and, according to one embodiment, is approximately100 kΩ. Resistor 278 is connected across node 284 and an anode of diode282 and, according to one embodiment, is approximately 10 to 20 Ω. Diode282 may, for example, be a Schottky diode having a turn on forward biasvoltage of approximately 0.5 V, and further has a cathode connected to areference voltage, such as ground 232. Resistor 280 is connected acrossnode 284 and a reference voltage, such as ground 232 and, according toone embodiment, is approximately 100 Ω. Bias control transistor 240comprises a bipolar transistor and has a collector connected to node 258and an emitter connected to node 284. Resistor 248 is connected across abase of bias control transistor 240 and Vcont 156 and, according to oneembodiment, is approximately 10 kΩ.

In operation, control circuit 206 operates in substantially the samemanner as described above in conjunction with control circuit 106 ofFIG. 1. Thus, as Vcont 256 is increased from a low level, bias controltransistor 240 is gradually turned on, resulting in a gradual increaseof collector current (“Ic”) 262 of bias control transistor 240. As Ic262 is gradually increased, Req of control circuit 206 is dynamicallyreduced such that control circuit 206 draws increased current 264, andas discussed above in conjunction with FIG. 1, further results inincreased Vb of amplifier transistor 110 at node 130, and in increasedIb 108 and Icq 112 of amplifier transistor 110. Due to the particulararrangement of control circuit 206, significantly improved analogcontrol over Vb of amplifier transistor 110 by control circuit 106 isachieved, such that continuous Icq 112 transition from a very low powerlevel can be provided, which results in significant current savings.

Control circuit 206 of FIG. 2 further includes resistor 278 and diode282 connected across node 284 and ground 232. In this particulararrangement, resistor 278 and diode 282 operate to reduce therequirement of having very high Vcont 252 for high mode operation.According to another embodiment, temperature compensation circuit 150 ofFIG. 1 could be connected between resistor 248 and the base of biascontrol transistor 240 of FIG. 2 to provide temperature compensation andimproved continuous control of quiescent current 112 of amplifiertransistor 110 as described above.

Referring now to FIG. 3, exemplary control circuit 306 according anotherembodiment of the present invention is shown. Control circuit 306 may beused to control bias circuit 102 of FIG. 1 and to provide continuouscontrol of quiescent current 112 of amplifier transistor 110 asdescribed above, wherein control circuit 306 replaces control circuit106 of FIG. 1.

In FIG. 3, Vcont 356, node 326, ground 332, bias control transistor 340and resistors 342, 344, 336 and 348 respectively correspond to Vcont156, node 126, ground 132, bias control transistor 140 and resistors142, 144, 136 and 148 in FIG. 1. Also shown in FIG. 3, temperaturecompensation circuit 350 is connected at node 360 to the base of biascontrol transistor 340. Temperature compensation circuit 350 comprisesresistor 352 and diodes 353 and 355. Resistor 352 is connected acrossnode 360 and an anode of diode 353. A cathode of diode 353 is connectedto an anode of diode 355, and a cathode of diode 355 is connected to areference voltage, such as ground 332. Diode 353 and 355 may, forexample, be Schottky diodes, each diode 353 and 355 having a turn onforward bias voltage of approximately 0.5 V. In this way, diodes 353 and355 have a functionally equivalent turn on forward bias voltage (i.e.,measured across the anode of diode 353 and the cathode of diode 355) ofapproximately 1 to 1.2 V. Thus, operation of control circuit 306operates in substantially the same manner described above in conjunctionwith control circuit 106 of FIG. 1.

In sum, a quiescent current control circuit for high-power amplifiers isachieved according to various embodiments of the present invention,whereby significant analog continuous control over the quiescent currentof an amplifier is achieved, resulting in significantly reduced currentand power consumption, particularly for low mode operation. Furthermore,improved temperature compensation is achieved by the control circuit ofthe present invention, resulting in improved control over the quiescentcurrent of an amplifier. Moreover, the control circuit of the presentinvention is based on bipolar technology, allowing the control circuitto be integrated into the same die as the bias circuit and theamplifier, resulting in significant cost savings and reduced devicesize.

From the above description of exemplary embodiments of the invention itis manifest that various techniques can be used for implementing theconcepts of the present invention without departing from its scope.Moreover, while the invention has been described with specific referenceto certain embodiments, a person of ordinary skill in the art wouldrecognize that changes could be made in form and detail withoutdeparting from the spirit and the scope of the invention. For example,the particular resistive values for bias circuit 102 and controlcircuits 106, 206 and 306 discussed above can be modified withoutdeparting from the scope of the present invention. The describedexemplary embodiments are to be considered in all respects asillustrative and not restrictive. It should also be understood that theinvention is not limited to the particular exemplary embodimentsdescribed herein, but is capable of many rearrangements, modifications,and substitutions without departing from the scope of the invention.

Thus, a quiescent current control circuit for high-power amplifiers hasbeen described.

1. A bias control circuit for a bias circuit, said bias circuit beingcoupled to an amplifier transistor, and further including a first biastransistor, a second bias transistor, and a third bias transistor, abase of said amplifier transistor being coupled to an emitter of saidsecond bias transistor, a base of said second bias transistor beingcoupled to a base of said first bias transistor and to a collector ofsaid third bias transistor, a base of said third bias transistor beingcoupled to an emitter of said first bias transistor and to said biascontrol circuit at a first node, said bias control circuit comprising:means for receiving a control voltage; and means for actively adjustingan equivalent resistance of said bias control circuit responsive to saidcontrol voltage, said equivalent resistance being established betweensaid first node and a reference voltage.
 2. The bias control circuit ofclaim 1, wherein said equivalent resistance is gradually decreased whensaid control voltage is increased.
 3. The bias control circuit of claim1, wherein a current drawn by said bias control circuit is graduallyincreased when said control voltage is increased.
 4. The bias controlcircuit of claim 1, wherein a quiescent current of said amplifiertransistor is gradually increased when said control voltage isincreased.
 5. The bias control circuit of claim 1, wherein said biascontrol circuit, said bias circuit and said amplifier transistor areintegrated into a single die.
 6. The bias control circuit of claim 1,wherein said amplifier transistor is a high-power CDMA transistor. 7.The bias control circuit of claim 1, wherein said reference voltage isground.
 8. A bias control circuit for a bias circuit, said bias circuitbeing coupled to an amplifier transistor, and further including a firstbias transistor, a second bias transistor, and a third bias transistor,a base of said amplifier transistor being coupled to an emitter of saidsecond bias transistor, a base of said second bias transistor beingcoupled to a base of said first bias transistor and to a collector ofsaid third bias transistor, a base of said third bias transistor beingcoupled to an emitter of said first bias transistor and to said biascontrol circuit at a first node, said bias control circuit comprising: abias control transistor having a base, a collector, and an emitter; afirst resistor connected across said collector of said bias controltransistor and said first node; a second resistor connected across saidcollector of said bias control transistor and a first reference voltage;a third resistor connected across said emitter of said bias controltransistor and said first reference voltage; and a fourth resistorconnected across a control voltage and said base of said bias controltransistor, wherein said bias control transistor actively adjusts anequivalent resistance of said bias control circuit responsive to saidcontrol voltage, said equivalent resistance being established betweensaid first node and said first reference voltage.
 9. The bias controlcircuit of claim 8, wherein each of said amplifier transistor, saidfirst bias transistor, said second bias transistor, said third biastransistor and said bias control transistor comprises a bipolartransistor.
 10. The bias control circuit of claim 9, wherein saidamplifier transistor, said first bias transistor, said second biastransistor, said third bias transistor and said bias control transistorare integrated into a single die.
 11. The bias control circuit of claim8, further comprising a fifth resistor connected across said base ofsaid first bias transistor and a second reference voltage, and a sixthresistor connected across said emitter of said second bias transistorand said first reference voltage.
 12. The bias control circuit of claim8, further comprising a temperature compensation circuit comprising afifth resistor and at least one diode, wherein a first end of said fifthresistor is connected to said base of said bias control transistor, asecond end of said fifth resistor is connected to an anode of said atleast one diode, a cathode of said at least one diode being connected tosaid first reference voltage.
 13. The bias control circuit of claim 12,wherein said at least one diode comprises an HBT diode.
 14. The biascontrol circuit of claim 8, further comprising a temperaturecompensation circuit comprising a fifth resistor and first and secondSchottky diodes, wherein a first end of said fifth resistor is connectedto said base of said bias control transistor, a second end of said fifthresistor is connected to an anode of said first Schottky diode, acathode of said first Schottky diode being connected to an anode of saidsecond Schottky diode, a cathode of said second Schottky diode beingconnected to said first reference voltage.
 15. A bias control circuitfor a bias circuit, said bias circuit being coupled to an amplifiertransistor, and further including a first bias transistor, a second biastransistor, and a third bias transistor, a base of said amplifiertransistor being coupled to an emitter of said second bias transistor, abase of said second bias transistor being coupled to a base of saidfirst bias transistor and to a collector of said third bias transistor,a base of said third bias transistor being coupled to an emitter of saidfirst bias transistor and to said bias control circuit at a first node,said bias control circuit comprising: a bias control transistor having abase, a collector, and an emitter; a first resistor connected acrosssaid collector of said bias control transistor and said first node; asecond resistor connected across said collector of said bias controltransistor and said emitter of said bias control transistor; a thirdresistor connected across said emitter of said bias control transistorand said first reference voltage; a fourth resistor connected acrosssaid emitter of said bias control transistor and an anode of a firstdiode, said first diode having a cathode connected to said firstreference voltage; a fifth resistor connected across a control voltageand said base of said bias control transistor, wherein said bias controltransistor actively adjusts an equivalent resistance of said biascontrol circuit responsive to said control voltage, said equivalentresistance being established between said first node and said firstreference voltage.
 16. The bias control circuit of claim 15, whereineach of said amplifier transistor, said first bias transistor, saidsecond bias transistor, said third bias transistor, and said biascontrol transistor comprises a bipolar transistor.
 17. The bias controlcircuit of claim 16, wherein said amplifier transistor, said first biastransistor, said second bias transistor, said third bias transistor, andsaid bias control transistor are integrated into a single die.
 18. Thebias control circuit of claim 15, further comprising a sixth resistorconnected across said base of said first bias transistor and a secondreference voltage, and a seventh resistor connected across said emitterof said second bias transistor and said first reference voltage.
 19. Thebias control circuit of claim 15, further comprising a temperaturecompensation circuit comprising a sixth resistor and at least oneadditional diode, wherein a first end of said sixth resistor isconnected to said base of said bias control transistor, a second end ofsaid sixth resistor is connected to an anode of said at least oneadditional diode, a cathode of said at least one additional diode beingconnected to said first reference voltage.
 20. The bias control circuitof claim 15, wherein said first reference voltage is ground.